The present invention relates to apparatus for effecting and controlling the movements of one or more components to a plurality of preselected positions, especially to apparatus for effecting and controlling angular movements of turrets or analogous tool supporting devices in machine tools to a plurality of positions in accordance with a predetermined program. The apparatus of the present invention can be utilized to effect and control the indexing of a tool turret which is mounted on a slide or carriage in a machine tool wherein a workpiece is rotated by a work spindle and can be treated by a plurality of tools in a predetermined sequence which necessitates repeated indexing of the turret to preselected angular positions in which certain tool or tools are in an optimum position with respect to the workpiece.
It is already known to utilize in a machine tool a computer or analogous programming means which can be set to automatically determine or select the movements of a turret or an analogous indexible tool supporting device to a series of predetermined angular positions. It is also known to utilize in such machine tools control apparatus which are responsive to signals from the programming means and serve to effect the movements of turret to successive angular positions.
The commonly owned German Offenlegungsschrift No. 2,110,147 discloses a control apparatus having means (hereinafter referred to as decoding unit) which insures that the turret can be indexed from a preceding position to the next position within a short interval of time by selecting the direction of rotation of the turret in such a way that the latter need not be indexed through more than 180.degree.. For example, and assuming that the turret is indexible between eight predetermined positions whereby the angular displacement of the turret from any one of the eight positions to one of the two neighboring positions involves rotation through an angle of 45.degree., the decoding unit insures that the turret can reach any selected position by rotating through an angle of 180.degree., 135.degree., 90.degree. or 45.degree..
The apparatus of the German Offenlegungsschrift No. 2,110,147 further comprises a control unit which includes means for indexing the turret and comprises a prime mover and at least one control element capable of regulating the speed of the prime mover so that the turret is rapidly indexed from the preceding position toward the next position but its speed is reduced shortly before it reaches the next position whereupon the speed of the prime mover decreases gradually to zero speed which is reached at the exact moment when the turret assumes the next position.
A drawback of the apparatus which is described in the just discussed German publication is that it must further comprise a relatively complex and bulky decelerating unit which serves to determine when the speed of the prime mover for the indexible turret is to be reduced from a higher to a lower speed. The decoding and decelerating units respectively comprise a plurality of discrete cams which can actuate electric switches. For example, each of these units can comprise four discrete rotary cams and four limit switches whereby the cams of the decoding unit are adjacent to and coaxial with the cams of the decelerating unit and the four switches of the decoding unit are aligned with the four switches of the decelerating unit. The cams rotate with the turret and together constitute an elongated cam drum.
The axial length of the drum is substantial so that it must be taken into consideration in dimensioning of the turret, i.e., the body or housing of the turret must be made larger for the specific purpose of accommodating the cams of the decoding and decelerating units.
Furthermore, the components of the decelerating unit contribute significantly to the initial and maintenance cost of the control apparatus. The positions of switches of the decelerating unit relative to the respective cams must be selected and maintained with an extremely high degree of accuracy so that such work must be performed by skilled operators. The construction of the control apparatus, especially of the aforementioned control element which effects the deceleration of prime mover for the turret to zero speed, also contributes excessively to the initial and maintenance cost of the control apparatus. The control element is a rotary valve member which must be machined and mounted with utmost precision in order to insure that the turret is invariably arrested at the exact moment when it assumes one of the predetermined angular positions. The rotary valve member comprises a ring which is rigidly mounted on the shaft of the turret and is provided with a plurality of pairwise arranged bores, one pair for each angular position of the turret. Each bore is parallel to the axis of the shaft for the turret. The bores of each pair are connected to discrete conduits for a hydraulic fluid, e.g., oil, whereby the fluid which is admitted via one bore of each pair effects clockwise rotation and the fluid which is admitted via the other bore of the respective pair effects counterclockwise rotation of the turret. The angular spacing of such bores must be highly accurate which is difficult to achieve, especially when the diameter of the ring is relatively small and also because the ring is likely to be distorted in response to changes in temperature. Even extremely minor deviations of the position of one or more bores from a predetermined position will affect the accuracy with which the turret is indexed to one or more angular positions with respect to its slide or carrier. When the speed of the prime mover for the turret is reduced, one or more bores in the aforementioned ring of the control element register with a stationary throttling passage which is connected with a conduit for return flow of hydraulic fluid at atmospheric pressure. Gradual deceleration of the prime mover to zero speed takes place as a result of the flow of hydraulic fluid through a portion of the aforementioned passage whose cross-sectional area decreases gradually. The just described control unit of the control apparatus is quite expensive and prone to malfunction, e.g., if the fluid contains solid impurities. Moreover, the control unit occupies a substantial amount of space which must be provided in addition to the space for the component parts of the aforediscussed decoding and decelerating units. As a rule, the turret is too small to accommodate all three units of the just described control apparatus so that several components of such units must be mounted on and/or adjacent to the shaft for the turret outside of the housing or body of the turret.